Earlier findings that 1) sleep deprivation might be beneficial in certain depressed patients and 2) that patterns of average evoked response (AER) were related to individual differences in sleep duration suggested the utility of the AER in clinical sleep deprivation studies. AER data were collected on normal controls, patients with affective illness and medication-free narcoleptics as a comparison. Primary affective disorder patients showed in increase in AER augmenting following sleep deprivation not shown by normal controls.